The present invention relates generally to cathodic arc coating and, more particularly, to an improved cooling system for cathodic arc cathodes.
The cathodic arc process is known in the art as a robust, relatively inexpensive technique for deposition of single and multi-component metallic and nonmetallic coatings. Cathodic arc deposition systems consist of a vacuum chamber which include an anode, a power supply and a cathode. The cathode material is deposited during the operation of the system.
Due to the large arc power needed for deposition, the heat generated must be removed from the cathode to prevent melting or other undesirable effects. In known cathodic arc source designs, the cathode is mounted to a cooling block in which water flows over the back surface of the cathode. However, at high currents the cathode may still overheat. Not only may an expensive sample be damaged but also a coolant failure may result in water flash vaporizing into the vacuum chamber, which may damage the entire coating apparatus and vacuum pump. In addition, the cooling system must be capable of, carrying the increased current load.
Thus, there remains a need for an improved cathodic arc coating apparatus which is able to handle the temperature created by much higher currents while, at the same time, providing sufficient electrical contact to conduct these high currents.
The present invention is directed to an apparatus for cathodic arc coating. The apparatus includes: a vacuum chamber which includes: an anode; a power supply; and a cathode target assembly connected to the power supply. The cathode target assembly has a channeled back surface for improving heat transfer from the cathode target.
In the preferred embodiment, the cathode target also includes a conductor segment connecting the cathode target to the power supply of the cathodic arc coating apparatus for conducting the increased current capacity of the cathode and a cooling block in contact with the cathode to further improve the heat transfer from the cathode target.
The cooling block includes a chamber adjacent to the cathode and a cooling fluid supply contained within the chamber. A fluid seal between the cooling block and the cathode prevents leakage of coolant into the vacuum chamber. The cooling fluid supply includes an inlet for providing cooling fluid into the chamber and an exit for withdrawing the fluid from the chamber.
The vacuum chamber includes an enclosed chamber and a staged pump for producing a vacuum therein. In the preferred embodiment, the power supply is a continuous DC power supply of greater than about 60 amps at about 20 volts.
In the preferred embodiment, the channeled back surface of the cathode target is continuous and annular. In addition, the cross-sectioned area of the conductor segment is sufficient to conduct at least 1 amp/cm2.
Accordingly, one aspect of the present invention is to provide an apparatus for cathodic arc coating. The apparatus includes: a vacuum chamber which includes an anode; a power supply; and a cathode target assembly located within the vacuum chamber and connected to the power supply, and having a channeled back surface for improving heat transfer from the cathode target.
Another aspect of the present invention is to provide an improved cathode target assembly for a cathodic arc coating apparatus. The cathode target assembly includes: a cathode target having a channeled back surface for improving heat transfer from the cathode target; and a conductor segment connecting the cathode target to the power supply of the cathodic arc coating apparatus.
Still another aspect of the present invention is to provide an apparatus for cathodic arc coating. The apparatus includes: a vacuum chamber which includes: an anode; a power supply; a cathode target assembly located within the vacuum chamber and connected to the power supply, and having a channeled back surface for improving heat transfer from the cathode target and a conductor segment connecting the cathode target to the power supply of the cathodic arc coating apparatus; and a cooling block in contact with the cathode target.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings.